1. Technical Field
The present invention relates generally to methods for high throughput screening of lubricating oil compositions.
2. Description of the Related Art
The use of a combinatorial approach for materials synthesis is a relatively new area of research aimed at using rapid synthesis and screening methods to build libraries of polymeric, inorganic or solid state materials. For example, advances in reactor technology have empowered chemists and engineers to rapidly produce large libraries of discrete organic molecules in the pursuit of new drug discovery, which have led to the development of a growing branch of research called combinatorial chemistry. Combinatorial chemistry generally refers to methods and materials for creating collections of diverse materials or compounds—commonly known as libraries—and to techniques and instruments for evaluating or screening libraries for desirable properties.
Presently, research in the lubricant industry involves individually forming candidate lubricating oil compositions and then performing a macro-scale analysis of the candidate compositions by employing a large amount of the candidate to be tested. Additionally, the methods employed for testing each candidate composition require manual operation. This, in turn, significantly reduces the number of compositions that can be tested and identified as leading compositions.
Drawbacks associated with conventional screening procedures can be seen as follows. For example, governmental and automotive industry pressure towards reducing the phosphorous and sulfur content of lubricating oil compositions used as, for example, passenger car and heavy duty diesel engine oils, is leading to new research to identify oil compositions which can satisfy certain tests such as, for example, oxidation, wear and compatibility tests, while containing low levels of phosphorous and sulfur. In this context, United States Military Standards MIL-L-46152E and the ILSAC Standards defined by the Japanese and United States Automobile Industry Association at present require the phosphorous content of engine oils to be at or below 0.10 wt. % with future phosphorous content being proposed to even lower levels, e.g., 0.08 wt. % by June, 2004 and below 0.05 wt. % by January, 2006. Also, at present, there is no industry standard requirement for sulfur content in engine oils, but it has been proposed that the sulfur content be below 0.3 wt. % to meet June, 2007 requirements for emissions. Thus, it would be desirable to decrease the amount of phosphorous and sulfur in lubricating oils still further, thereby meeting future industry standard proposed phosphorous and sulfur contents in the engine oil while still retaining the oxidation or corrosion inhibiting properties and antiwear properties of the higher phosphorous and sulfur content engine oils. In order to accomplish this, a large number of proposed lubricating oil compositions must be tested to determine which compositions may be useful.
Additionally, similar changes in specifications and changing customer needs also drive reformulation efforts in other lubricant applications such as, for example, transmission fluids, hydraulic fluids, gear oils, marine cylinder oils, compressor oils, refrigeration lubricants and the like.
However, as stated above, present research in the lubricant industry does not allow for reformulation to occur in an expeditious manner. As such, there exists a need in the art for a more efficient, economical and systematic approach for the preparation of lubricating oil compositions and screening of such compositions. For example, a problem facing lubricant manufacturers is that of seal deterioration in the engine. All internal combustion engines use elastomer seals such as, for example, viton seals, in their assembly. During use, these elastomer seals are susceptible to serious deterioration from lubricating oil additive compositions and lubricating oil compositions under engine operating conditions. Deterioration in the seals results in brittleness and cracking of the seals causing oil to leak from the engine. A lubricating oil composition that degrades the elastomer seals in an engine is unacceptable to engine manufacturers.
Another example of elastomer compatibility is in elastomeric electrical cable accessories which are installed, for example, over cables, metallic contacts or mated in complimentary designs such as elbows and bushings, connectors, splices, switches, fuses, junctions and a wide variety of other configurations. Cable accessories are usually based on ethylene-propylene elastomers, e.g., ethylene-propylene rubber (EPR) and ethylene propylene diene monomer (also referred to as ethylene propylene diene methyl or EPDM), and are typically lubricated with silicone-based oils and greases. In almost every design, installation requires interfaces to slide against each other with corresponding frictional forces. Because these components are elastomeric, these frictional forces are very high. Thus lubrication of these interfaces is a necessity. The most common lubricants are oils and greases, typically based on a compatibility with the type of elastomer requiring lubrication. Silicone oils and greases exhibit excellent electrical characteristics and are very compatible with ethylene-propylene based elastomers. These lubricants are usually supplied by the manufactures at significant cost as a separate package with the cable accessories.
Generally, cable accessories have approximately a thirty to forty year life span, and many have separable interfaces used for connection and disconnection. Although many oils and greases are high quality and are used effectively for many years of service, they often lose their lubricating capacity over time. Due to the inherent mobility of the oils used in these lubricants, they tend to “bleed” and/or migrate away from the interface. Consequently, the interface “dries out” and exposes the high coefficient of friction elastomeric surface. The result is component sticking which is a major problem in the industry.
Accordingly, it would be desirable to rapidly screen a plurality of sample candidate lubricating oil compositions for compatibility with elastomers utilizing small amounts of each sample. In this manner, a high throughput preparation and screening of a vast number of diverse compositions can be achieved to identify which compositions are substantially compatible with elastomers.